The present invention relates to a power control system for a vehicle, which is equipped with a torque converter and enabled to control the engine torque independently of an accelerator pedal.
At the time of an engine stall under a high load when the brake pedal and the accelerator pedal are simultaneously depressed, generally speaking the load to be applied to the drive train is considerably higher than that to be applied for the ordinary start and acceleration. This requires a stronger--and so heavier--drive train. It has been conceived to lessen the weight of the drive train including the automatic transmission by reducing the engine torque automatically under such circumstances, to lighten the load upon the drive train.
This concept is exemplified by SAE Paper 870081 disclosing the technology which is directed to an engine control system for an automobile using an automatic transmission. According to this technology, the weight of the automatic transmission can be lessened by lightening the load to be applied to the automatic transmission. Specifically, the engine torque is determined at first from the flow rate of intake air of the engine and is then multiplied by the torque ratio of the torque converter to calculate the input torque of the transmission. Thus, the engine torque is reduced by controlling the ignition timing such that the input torque of the transmission does not exceed an allowed maximum value of the transmission.
Since, however, the flow rate of intake air of the engine and the engine torque are not proportional in a transient state wherein the flow rate of intake air is abruptly varied, an error is naturally caused by the method of determining the engine torque from the flow rate of intake air. More specifically, the flow rate of intake air of the engine is generally measured by means of an air flow meter. The flow rate of intake air is increased as soon as the accelerator pedal is depressed at a certain or higher rate. Even if this increase is detected, the rise of the engine torque is considerably delayed from the detection, because the intake air has to pass through a portion having a large capacity such as a surge tank interposed between the air flow meter and the engine.
Since, in this transient state, the rise of the engine torque is considerably delayed from the increase in the intake air flow rate, the calculation of the engine torque on the basis of the flow rate results in a large error.
In the above-specified method of the prior art, moreover, the inertia of the rotary components of the engine and/or the torque converter is not especially considered for calculating the input torque to be applied to the automatic transmission. The inertial torque of those rotary components also augments the error at the rising time of the speed of revolution of the engine. Thus, there arises another problem that excess input torque of the automatic transmission is calculated, the excess corresponding to the error augmentation. In case the engine output is increased to raise the number of revolutions, the torque increase is partially consumed by the change of the number of revolutions of the rotary components so that the input torque to the automatic transmission is accordingly decreased. In the prior art, however, the inertial torque of the rotary components is not taken into account for the calculation. The value of the input torque obtained thus higher than the actual value, thus raising a further problem that an unnecessary control is executed to drop the torque.